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Corn Newsletter : 2018-19
Reminders about dicambaAuthor(s): Mark Loux
This is the time of year when we received our first call about dicamba problems in soybeans in 2017. We can probably expect any problems to become evident soon, based on the timing of postemergence applications and timeline for development of symptoms. Off-target issues have already developed in states farther west and south, and we would expect at least some to occur here, unless we’re really lucky. The symptoms of dicamba injury show in new soybean growth within approximately 7 to 21 days after exposure, and most of our soybeans receive postemergence applications from early June on. It’s been a challenging year to properly steward postemergence applications. We still face some challenges in finding appropriate weather to catch weeds before they become too large, and before soybeans are too advanced in growth stage. There are a number of weather, application and adjacent crop factors to consider when applying dicamba, and applicators should review labels as frequently as needed to ensure legal application.
We have two requests relative to reporting of off-target dicamba issues. First, we ask that if at all possible, they be reported to ODA. It is important for ODA to have a record of these, in order to be able to make sound decisions on mitigating risk from dicamba as we move forward, or decide that no additional mitigation is necessary. Reporting to ODA allows them to be able to investigate the cause of off-target issues, and develop first-hand knowledge that can aid in making these decisions. As we ask this, know that we are fully aware of the reasons why off-target injury issues are not reported to ODA. The companies involved are once again at least talking a good game about investigating dicamba issues that are reported to them, and we would certainly encourage reporting any incidents to them also. Experience in 2017 would indicate that for at least one company, on-site investigations occurred only if reported by the party who purchased and applied the dicamba product. Reporting only by the affected party did not warrant the same level of investigation. Maybe this has changed.
The second request concerns how OSU Extension staff and clientele communicate anything pertaining to off-target dicamba problems to OSU Weed Science, including Mark Loux. Due to litigation on dicamba occurring somewhere beside Ohio, OSU has been subject to an open records request asking us to provide files we have related to our experience with dicamba – off-target investigations, research, etc. First time in my career this has occurred. In addition to the time we will have to put in to deal with this, there’s just the general hassle of it all. There is also another aspect - we cannot necessarily protect the confidentiality of anyone sending emails to us. My specific request is this – from this point on please do not send anything in written or electronic form to us about dicamba, including emails, photos, etc. Should you need to contact us about a dicamba issue, please feel free to call. We still want to provide information and service on this issue, and are certainly not trying to shut off communication. Moving forward, we are just trying to avoid maintaining any type of records that could be asked for in this type of request. Fun times to be an extension weed specialist.
Hot streak ahead!Author(s): Jim Noel
After a really wet period last week and even some flooding in northwest Ohio, we will be seeing a switch toward hotter weather and a drier window from Thursday into the weekend.
We have had a few hot bursts this summer but nothing like the stretch ahead. So far May and June have been warmer and wetter than normal in most places. It looks like after one more round of showers and a few storms the middle of this week it will turn hot for the end of June. This heat will last into the first half of July before relaxing some for the second half of July. There may a a day or two break from time to time during the warm weather the next few weeks but above normal temperatures will rule into July.
Rainfall also looks to relax more toward the normal range but with longer stretches of dryness mixed in with the wetness.
The outlook for the remainder of June calls for temperatures to average 3-5 degrees above normal. Rainfall will average 0.50-1.0 inches for the last week of June which is close to normal or slightly below normal. The outlook for the first week of July calls for temperatures to average 6-8 degrees above normal with highs mostly 85-95. Lows will be 65-75. Rainfall will average 0.25 to 1.00 inches which again is normal to below normal for most of Ohio. The outlook for the rest of July (weeks 2-4) calls for temperatures 1-3 degrees above normal and rainfall of 1-4 inches. Normal highs in Ohio are 80-85 and normal lows are 60-65. Rainfall normally average near 1 inch per week.
Looking further ahead in the growing season and harvest season, it appears August will still see slightly above normal temperatures and slightly below normal rainfall. September looks near normal temperatures and normal or slightly wetter than normal. Finally, October appears to be about normal temperatures and slightly drier than normal. For the latest 2 weeks rainfall predictions, see the graphic from the NOAA/NWS/Ohio River Forecast Center using the North American Ensemble Forecasting System average rainfall.
We have found some whiskers! (Spores of Cercospora sojina)
Last week, samples of frogeye leaf spot of soybean were brought into the lab. On the underside of the characteristic lesion were the conidia. This came from an area where the incidence of frogeye was notable at the end of the season. For the 2018 season a susceptible variety was planted back into that same field. Environmental conditions have been favorable for this disease to begin in some areas of the state. However, most of the varieties in the state have very good levels of resistance to this disease and if good rotation is practiced it will take more time for enough inoculum to build up to begin to move around the state.
There are numerous fungicides available for this foliar pathogen and in Ohio, but the caution here is the the strobilurins. Based on sampling over the past 3 years, the samples of this fungus in 2017 (last year) indicated that most of the populations were now resistant to the strobilurin based fungicides. We will begin testing any samples received this year in earnest, but based on last year’s sampling, farmers who are managing this disease should focus on using a triazole (FRAC Group 3) or a MBC Thiophanate (FRAC Group 1, thiophanate methyl) at the higher rates if disease is active in the field. The best timing is one spray at R3, at the end of flowering. This fungus will only infect young newly expanding leaves, so the goal in the spraying is to protect those big flushes of leaves as our indeterminant soybeans really fill out. Fungicide coverage should focus on the upper third of the canopy for this disease.
Other soybean diseases to keep in mind.
- Early and mid-season Phytophthora. With each of these saturating rains, soybeans that have low levels of partial resistance, (tolerance) will continue to develop Phytophthora stem rot. Last week at North West Branch the susceptible variety was dying all over the field. At this point, the plant should be able to hold its own against this pathogen if the resistance package is there. Make notes if it is not and choose a variety with better resistance scores for 2019.
- White mold caused by Sclerotinia stem rot. Cool nights and random rains to keep the moisture levels up are perfect for this disease of soybean. However, only in historically infested fields and only if the canopy is closed at those first flowers and most often on highly susceptible cultivars. So double check your variety ratings that got planted in those areas with a history of white mold. Based on a very large study by my team, resistant varieties did not need the fungicide and the fungicides that have worked were boscalid and picoxystrobin. Do not use other strobilurins in these fields as those have enhanced disease development. One application at first flower or right before (1 to 2 days) provided the best management of this disease on highly susceptible varieties.
Impact of ponding and saturated soils on corn
Persistent rains during the past two weeks have resulted in ponding and saturated soils in many Ohio corn fields and led to questions concerning what impact these conditions will have on corn performance.
The extent to which ponding injures corn is determined by several factors including: (1) plant stage of development when ponding occurs, (2) duration of ponding and (3) air/soil temperatures. Corn is affected most by flooding at the early stages of growth (see https://agcrops.osu.edu/newsletter/corn-newsletter/2018-15/young-corn-wet-feet-what-can-we-expect). Once corn has reached the late vegetative stages, saturated soil conditions will usually not cause significant damage. Since most corn in Ohio is approaching the late vegetative stages, this bodes well. Although standing water is evident in fields with compacted areas, ponding has usually been of limited duration (i.e. the water has drained off quickly within a few hours). Past work has indicated <10% yield loss when corn was flooded for 2 days or less. Moreover, temperatures have been moderate which will minimize the level of stress. If the rain has been paired with strong winds, root lodging may occur. Yield losses of 4, 10, and 15-25% reported for 100% root lodging at V10, V13-15, and V17-R1, respectively in Wisconsin. These values are currently being re-evaluated for Ohio by OSU researchers.
Past research at Iowa State University evaluated flood damage to corn that was inundated for variable periods of time at different stages of growth (including silking). Two different N levels ("high" N ‑ 350 lb N/ac vs. "low" N‑50 lb N/ac) were also considered to determine how N affected corn response to flood injury. Corn that was flooded when 30” tall (approximately V6) experienced a 6-8% reduction under high N, and a 15-30% yield reduction under low N. Low N plots yields were reduced by 16% at silking when plots were flooded for 96 and 72 hours. In the high N plots, flooding at silking had little or no effect on yields.
However, under certain conditions saturated soils can result in yield losses. Although plants may not be killed outright by the oxygen deficiency and the carbon dioxide toxicity that result from saturated soils, root uptake of nutrients may be seriously reduced. Root growth and plant respiration slow down while root permeability to water and nutrient uptake decreases. Impaired nutrient uptake may result in deficiencies of nitrogen and other nutrients during the grain filling stage. Moreover, saturated soil conditions can also result in losses of nitrogen through denitrification and leaching.
According to Dr. Emerson Nafziger at the University of Illinois (http://bulletin.ipm.illinois.edu/?p=1240) “…At the time the crop reaches stage V13 (about head-high), it still has to take up 110 to 120 lb of N, and in years when June is wet, a common question is whether or not the crop might run out of nitrogen, leaving the crop short. While the need for 20 or more lb of N per week would seem to raise the possibility of a shortage, the production of plant-available N from soil organic matter through the process of mineralization is also at its maximum rate in mid-season. For a crop with a good root system growing in a soil with 3 percent organic matter, mineralization at mid-season likely provides at least half the N needed by the crop on a daily basis. This means that normal amounts of fertilizer N, even if there has been some loss, should be adequate to supply the crop.”
Carter, P.R. and K.D. Hudelson. 988. Influence of simulated wind lodging on corn growth and grain yield. J. Prod. Agric. 1:295-299.
Kaur, G., B.A. Zurweller, K.A. Nelson, P.P. Motavalli, and C.J. Dudenhoeffer. 2017. Soil waterlogging and nitrogen fertilizer management effects on corn and soybean yields. Agron. J. 109:1-10.
Ritter, W.R. and Beer, C.E. 1969. Yield reduction by controlled flooding of corn. Trans. ASAE 12:46-47.
Application of Manure to Double Crop SoybeansAuthor(s): Glen Arnold, CCA
Wheat fields will be harvested in Ohio soon and some farmers will plant double-crop soybeans. In recent years there has been more interest from livestock producers in applying manure to newly planted soybeans to provide moisture to help get the crop to emerge.
Both swine and dairy manure can be used to add moisture to newly planted soybeans. It’s important that the soybeans were properly covered with soil when planted to keep a barrier between the salt and nitrogen in the manure and the germinating soybean seed. It’s also important that livestock producers know their soil phosphorus levels, and the phosphorus in the manure being applied, so soil phosphorus levels are kept an acceptable range.
An acre-inch of water is 27,154 gallons. The application of 10,000 gallons per acre of dairy manure would be about 0.37 inches of moisture. The application of 7,000 gallons of swine manure would be about 0.26 inches of moisture. While we strongly encourage the incorporation of livestock manure whenever possible, the use of manure to help with double-crop soybean emergence does not really allow for incorporation.
If soybeans are emerged, swine finishing manure is likely to kill the emerged plants. Swine nursery manure and sow manure are unlikely to kill emerged soybeans. We are starting manure drag hose research at two of our Ohio Agricultural Research and Development Center stations. The manure hose has not appeared to cause much damage to emerged soybeans at the V1, V3, and V5 stages. We will take stand counts and yield data this fall to determine if the soybean yields were impacted.
If manure is incorporated prior to planting double-crop soybeans be sure the manure salt and nitrogen is not placed in the planting zone. Placing the manure in contact with germinating seeds can result in severe emergence problems.
As always, print out the weather forecast when surface applying manure. Remember the “not greater than 50% chance of 0.5 inches of rainfall in the next 24 hours” rule in the Western Lake Erie Basin.
About the C.O.R.N. Newsletter
C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.
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